function show_sub_menu(element) {
	var sub_menu = element.querySelector('div.sub-menu');
	sub_menu.style.visibility = "visible"
	sub_menu.style.opacity = "1";
}

function hide_sub_menu(element) {
	var sub_menu = element.querySelector('div.sub-menu');
	sub_menu.style.opacity = "0";
	sub_menu.style.visibility = "hidden"
}
